U.S. patent application number 16/724485 was filed with the patent office on 2020-07-02 for fluoride fluorescent material, light emitting device, and method for producing fluoride fluorescent material.
This patent application is currently assigned to NICHIA CORPORATION. The applicant listed for this patent is NICHIA CORPORATION. Invention is credited to Tomokazu YOSHIDA.
Application Number | 20200208050 16/724485 |
Document ID | / |
Family ID | 69410936 |
Filed Date | 2020-07-02 |
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United States Patent
Application |
20200208050 |
Kind Code |
A1 |
YOSHIDA; Tomokazu |
July 2, 2020 |
FLUORIDE FLUORESCENT MATERIAL, LIGHT EMITTING DEVICE, AND METHOD
FOR PRODUCING FLUORIDE FLUORESCENT MATERIAL
Abstract
A fluoride fluorescent material includes a composition including
K, Ge, Mn.sup.4+, and F and having a molar ratio of K of 2, a total
molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio of Mn.sup.4+ of
more than 0 and less than 0.2, and a molar ratio of F of 6 in 1 mol
of the composition, has a light emission spectrum having a first
light emission peak in a range of 615 nm or more and less than 625
nm having a full width at half maximum of 6 nm or less, and a
second light emission peak in a range of 625 nm or more and less
than 635 nm, and has an internal quantum of 85% or more efficiency
under excitation of light having a wavelength of 450 nm.
Inventors: |
YOSHIDA; Tomokazu;
(Anan-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi |
|
JP |
|
|
Assignee: |
NICHIA CORPORATION
Anan-shi
JP
|
Family ID: |
69410936 |
Appl. No.: |
16/724485 |
Filed: |
December 23, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/677 20130101;
H01L 2933/0041 20130101; H01L 33/507 20130101; C09K 11/665
20130101; H01L 33/502 20130101 |
International
Class: |
C09K 11/67 20060101
C09K011/67; H01L 33/50 20060101 H01L033/50 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2018 |
JP |
2018-243489 |
Claims
1. A fluoride fluorescent material comprising a composition
comprising K, Ge, Mn.sup.4+, and F and having a molar ratio of K of
2, a total molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio of
Mn.sup.4+ of more than 0 and less than 0.2, and a molar ratio of F
of 6 in 1 mol of the composition, the fluoride fluorescent material
having a light emission spectrum having a first light emission peak
in a range of 615 nm or more and less than 625 nm having a full
width at half maximum of 6 nm or less, and a second light emission
peak in a range of 625 nm or more and less than 635 nm, and having
an internal quantum efficiency of 85% or more under excitation of
light having a wavelength of 450 nm.
2. The fluoride fluorescent material according to claim 1, wherein
the composition is represented by the following formula (I):
K.sub.2[Ge.sub.1-aMn.sup.4+.sub.aF.sub.6] (I) wherein a satisfies
0<a<0.2.
3. The fluoride fluorescent material according to claim 1, having a
light emission intensity of 30% or more at the first light emission
peak based on the light emission intensity at the second light
emission peak as 100%.
4. The fluoride fluorescent material according to claim 1, having a
hexagonal crystal structure and having P63mc space group
symmetry.
5. The fluoride fluorescent material according to claim 1, wherein
the internal quantum efficiency under excitation of light having a
wavelength of 450 nm is 90% or more.
6. A light emitting device comprising the fluoride fluorescent
material according to claim 1 and an excitation light source having
a light emission peak in a range of 380 nm or more and 485 nm or
less.
7. The light emitting device according to claim 6, further
comprising a fluorescent material having a light emission peak
wavelength in a range of 495 nm or more and 573 nm or less.
8. A method for producing a fluoride fluorescent material,
comprising: preparing fluoride particles comprising a composition
comprising K, Ge, Mn.sup.4+, and F, and having a molar ratio of K
of 2, a total molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio
of Mn.sup.4+ of more than 0 and less than 0.2, and a molar ratio of
F of 6 in 1 mol of the composition; and bringing the fluoride
particles into contact with a fluorine-containing substance, and
subjecting to a heat treatment at a temperature of 400.degree. C.
or more.
9. The method for producing a fluoride fluorescent material
according to claim 8, wherein the fluoride particles are subjected
to the heat treatment in an inert gas atmosphere containing
nitrogen.
10. The method for producing a fluoride fluorescent material
according to claim 8, wherein the fluorine containing substance is
at least one selected from the group consisting of F.sub.2,
CHF.sub.3, CF.sub.4, NH.sub.4HF.sub.2, NH.sub.4F, SiF.sub.4, and
NF.sub.3.
11. The method for producing a fluoride fluorescent material
according to claim 8, wherein the composition is represented by the
following formula (I): K.sub.2[Ge.sub.1-aMn.sup.4+.sub.aF.sub.6]
(I) wherein in the formula (I), a satisfies 0<a<0.2.
12. The method for producing a fluoride fluorescent material
according to claim 8, wherein the fluoride fluorescent material has
an internal quantum efficiency of 85% or more under excitation of
light having a wavelength of 450 nm.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application claims priority to Japanese Patent
Application No. 2018-243489, filed on Dec. 26, 2018, the disclosure
of which is hereby incorporated reference in its entirety.
BACKGROUND
Technical Field
[0002] The present disclosure relates to a fluoride fluorescent
material, a light emitting device using the same, and a method for
producing a fluoride fluorescent material.
Description of Related Art
[0003] Various light emitting devices have been developed that emit
light in white color, bulb color, orange color, through combination
of a light emitting element, such as a light emitting diode (LED),
and a fluorescent material. The light emitting device of this type
emits mixed light in white color by mixing red light, green light,
and blue light, i.e., the three primary colors of light, through
combination, for example, of a light emitting device that emits
light on the short wavelength side corresponding to ultraviolet
light to visible light, and fluorescent materials that emit red,
green, and blue light. The light emitting device of this type is
being used in a wide variety of fields including general
illuminations, vehicle illuminations, displays, backlights for
liquid crystal display devices. For example, the fluorescent
material that is used in a light emitting device for the purpose of
a backlight for a liquid crystal display device is demanded to have
a good chromatic purity, i.e., a small full width at half maximum
of the light emission peak, for reproducing a wide range of colors
in the chromaticity coordinates. The full width at half maximum
means the full width at half maximum (FWHM) of the light emission
peak in the light emission spectrum, which means the wavelength
width of the light emission peak at 50% of the maximum value of the
light emission peak in the light emission spectrum.
[0004] As the fluorescent material that emits red light having a
small full width at half maximum, for example, Japanese Unexamined
Patent Publication No. 2010-209311 describes a fluoride fluorescent
material having a composition represented by
K.sub.2SiF.sub.6:Mn.sup.4+. NPL 1 describes the light emission
mechanism of a fluoride fluorescent material activated with
Mn.sup.4+.
CITATION LIST
Non-Patent Literature
[0005] NPL 1: A. G. Paulusz, "Efficient Mn(IV) Emission in Fluorine
Coordination", J. Electrochem. Soc.; SOLID-STATE SCIENCE AND
TECHNOLOGY, Vol. 120, No. 7, 1973, p. 942-947
SUMMARY
[0006] There has been a demand of further enhancement of the light
emission intensity of the fluoride fluorescent material emitting
red light activated with Mn.sup.4+.
[0007] Under the circumstances, an embodiment of the present
disclosure provides a fluoride fluorescent material having an
enhanced light emission intensity, a light emitting device using
the same, and a method for producing a fluoride fluorescent
material.
[0008] The present disclosure encompasses the following
embodiments.
[0009] A first embodiment of the present disclosure relates to a
fluoride fluorescent material including a composition including K,
Ge, Mn.sup.4+, and F and having a molar ratio of K of 2, a total
molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio of Mn.sup.4+ of
more than 0 and less than 0.2, and a molar ratio of F of 6 in 1 mol
of the composition, the fluoride fluorescent material having a
light emission spectrum having a first light emission peak in a
range of 615 nm or more and less than 625 nm having a full width at
half maximum of 6 nm or less, and a second light emission peak in a
range of 625 nm or more and less than 635 nm, and having an
internal quantum efficiency of 85% or more under excitation of
light having a wavelength of 450 nm.
[0010] A second embodiment of the present disclosure relates to a
light emitting device including the aforementioned fluoride
fluorescent material and an excitation light source having a light
emission peak in a range of 380 nm or more and 485 nm or less.
[0011] A third embodiment of the present disclosure relates to a
method for producing a fluoride fluorescent material, including:
preparing fluoride particles including a composition including K,
Ge, Mn.sup.4+, and F and having a molar ratio of K of 2, a total
molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio of Mn.sup.4+ of
more than 0 and less than 0.2, and a molar ratio of F of 6 in 1 mol
of the composition; and bringing the fluoride particles into
contact with a fluorine-containing substance, and subjecting to a
heat treatment at a temperature of 400.degree. C. or more.
[0012] According to the aforementioned embodiments, a fluoride
fluorescent material having an enhanced light emission intensity, a
light emitting device using the same, and a method for producing a
fluoride fluorescent material can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic cross sectional view showing an
example of a light emitting device using a fluoride fluorescent
material.
[0014] FIG. 2 is a light emission spectrum of the fluoride
fluorescent material of Example 1 of the present disclosure.
[0015] FIG. 3 is a light emission spectrum of the fluoride
fluorescent material of Comparative Example 1 of the present
disclosure.
[0016] FIG. 4 shows X-ray diffraction patterns of the fluoride
fluorescent materials of Example 1 and Comparative Example 1 of the
present disclosure.
[0017] FIG. 5 shows an X-ray diffraction pattern of the fluoride
fluorescent material of Example 1 of the present disclosure and an
X-ray diffraction pattern of the crystal structure model of
K.sub.2MnF.sub.6 according to ICDD Card No. 01-077-2133.
[0018] FIG. 6 is the light emission spectrum of the fluoride
fluorescent material of Reference Example 1.
[0019] FIG. 7 is a light emission spectrum of the fluoride
fluorescent material of Reference Example 2.
[0020] FIG. 8 shows X-ray diffraction patterns of the fluoride
fluorescent materials of Reference Example 1 and Reference Example
2.
DETAILED DESCRIPTION
[0021] The fluoride fluorescent material, the light emitting device
using the same, and the method for producing a fluoride fluorescent
material according to the present disclosure will be described with
reference to embodiments below. However, the embodiments shown
below are examples for substantiating the technical concept of the
present disclosure, and the present disclosure is not limited to
the fluoride fluorescent material, the light emitting device using
the same, and the method for producing a fluoride fluorescent
material shown below. The relationships between the color names and
the color coordinates, the relationships between the wavelength
ranges of light and the color names of monochromatic light, and the
like are in accordance with JIS Z8110.
Fluoride Fluorescent Material
[0022] The fluoride fluorescent material has a composition
containing K, Ge, Mn.sup.4+, and F, and has a molar ratio of K of
2, a total molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio of
Mn.sup.4+ of more than 0 and less than 0.2, and a molar ratio of F
of 6, in 1 mol of the composition, has a light emission spectrum
having a first light emission peak in a range of 615 nm or more and
less than 625 nm having a full width at half maximum of 6 nm or
less, and a second light emission peak in a range of 625 nm or more
and less than 635 nm, and has an internal quantum efficiency under
excitation of light having a wavelength of 450 nm of 85% or
more.
[0023] The fluoride fluorescent material preferably has a
composition represented by the following formula (I):
K.sub.2[Ge.sub.1-aMn.sup.4+.sub.aF.sub.6] (I)
[0024] wherein in the formula (I), a satisfies 0<a<0.2.
[0025] Although the mechanism of the first light emission peak in a
range of 615 nm or more and less than 625 nm having a full width at
half maximum of 6 nm or less in the light emission spectrum of the
fluoride fluorescent material, in addition to the second light
emission peak in a range of 625 nm or more and less than 635 nm, is
not clear, the crystal structure thereof is different from a
fluoride fluorescent material that has no first light emission
peak. As the cause of the difference of the crystal structure, it
is considered that the crystal structure is changed by the
influence of a heat treatment. In the case where fluoride particles
including a composition that contains K, Ge, Mn.sup.4+, and F but
does not contain Si are subjected to a heat treatment at a
temperature of 400.degree. C. or more, the K.sub.2GeF.sub.6 crystal
structure of the fluoride particles is changed to a crystal
structure similar to the K.sub.2MnF.sub.6 crystal structure. The
fluoride particles having a composition which does not contain Si
mean that the fluoride particles are substantially free of Si in
the composition of the fluoride particle. Specifically, Si content
in the composition of the fluoride particle may be 200 ppm by mass
or less, 100 ppm by mass or less, or 50 ppm by mass or less with
respect to 100% by mass of the fluoride particle. The light
emission spectrum of the fluoride fluorescent material obtained
based on the crystal structure thus changed has a first light
emission peak in a range of 615 nm or more and less than 625 nm
having a full width at half maximum of 6 nm or less, and a second
light emission peak in a range of 625 nm or more and less than 635
nm. The light emission component due to the first light emission
peak among these is added to the light emission spectrum of the
fluoride fluorescent material, and thereby a higher light emission
intensity than the fluoride fluorescent material containing Si in
the composition thereof can be obtained.
[0026] In the case where the composition of the fluoride
fluorescent material contains Ge and Si, a distorted crystal
structure is formed since in Ge and Si constituting the skeleton of
the crystal structure, the ionic radius of Si is considerably
smaller than the ionic radius of Ge or the ionic radius of
Mn.sup.4+ as the activation element. In the case where the
composition of the fluoride fluorescent material contains not only
Ge but also Si, even though the light emission spectrum has a first
light emission peak in a range of 615 nm or more and less than 625
nm, there may be cases where the light emission intensity at the
first light emission peak is decreased as compared to the fluoride
fluorescent material containing no Si in the composition thereof,
thereby failing to provide a high light emission intensity as the
fluoride fluorescent material.
[0027] The fluoride fluorescent material preferably has a hexagonal
crystal structure and preferably has P63mc space group symmetry.
The crystal structure and the space group of the fluoride
fluorescent material can be quantitatively determined by the RIR
(reference intensity ratio) method in the measurement by the powder
X-ray diffraction (XRD) method using CuK.alpha. line.
[0028] For example, a fluoride fluorescent material that has a
composition represented by
K.sub.2[Ge.sub.1-aMn.sup.4+.sub.aF.sub.6] (wherein a satisfies
0<a<0.2) and has no first light emission peak in a range of
615 nm or more and less than 625 nm in the light emission spectrum
has a hexagonal crystal structure and has P-3 m1 space group
symmetry. The difference in crystal structure between the fluoride
fluorescent material that has the first light emission peak in a
range of 615 nm or more and less than 625 nm in the light emission
spectrum and the fluoride fluorescent material that has no first
light emission peak in a range of 615 nm or more and less than 625
nm in the light emission spectrum can be confirmed from the
difference in space group of the crystal phase. It is estimated
that the fluoride fluorescent material having the first light
emission peak in a range of 615 nm or more and less than 625 nm
having a full width at half maximum of 6 nm or less, and the second
light emission peak in a range of 625 nm or more and less than 635
nm, in the light emission spectrum becomes closer to the crystal
structure of K.sub.2MnF.sub.6 than the crystal structure of
K.sub.2GeF.sub.6 through the heat treatment at a temperature of
400.degree. C. or more.
[0029] The fluoride fluorescent material has an internal quantum
efficiency under excitation of light having a wavelength of 450 nm
of 85% or more, preferably 90% or more, and more preferably 95% or
more. The fluoride fluorescent material has the first light
emission peak in a range of 615 nm or more and less than 625 nm
having a full width at half maximum of 6 nm or less, and a second
light emission peak in a range of 625 nm or more and less than 635
nm, in the light emission spectrum, and thereby has a high light
emission intensity and a high internal quantum efficiency under
excitation of light having a wavelength of 450 nm of 85% or
more.
[0030] The fluoride fluorescent material preferably has a light
emission intensity of 30% or more, more preferably 35% or more, and
further preferably 37% or more at the first light emission peak in
a range of 615 nm or more and less than 625 nm, based on the light
emission intensity at the second light emission peak in a range of
625 nm or more and less than 635 nm as 100%. In the case where the
light emission intensity at the first light emission peak is 30% or
more based on the light emission intensity at the second light
emission peak as 100%, the light emission intensity can be further
enhanced.
[0031] The fluoride fluorescent material has a full width at half
maximum of the first light emission peak in a range of 615 nm or
more and less than 625 nm in the light emission spectrum of 6 nm or
less, and preferably 5 nm or less. Accordingly, the fluoride
fluorescent material can emit light that has a good chromatic
purity and a high light emission intensity. The fluoride
fluorescent material may have a full width at half maximum of the
first light emission peak of 1 nm or more. The fluoride fluorescent
material preferably has a full width at half maximum of the second
light emission peak in a range of 625 nm or more and less than 635
nm in the light emission spectrum of 10 nm or less, and more
preferably 8 nm or less. The fluoride fluorescent material may have
a full width at half maximum of the second light emission peak of 1
nm or more. In the light emission spectrum of the fluoride
fluorescent material, the second light emission peak in a range of
625 nm or more and less than 635 nm as the main peak may sometimes
overlap a subsidiary peak around 635 nm, and in this case, it may
be difficult to measure the full width at half maximum of the
single light emission peak. In the light emission spectrum of the
fluoride fluorescent material, even in the case where the second
light emission peak in a range of 625 nm or more and less than 635
nm and the subsidiary peak partially overlap each other, the second
light emission peak in a range of 625 nm or more and less than 635
nm preferably has a full width at half maximum of 10 nm or
less.
Light Emitting Device
[0032] The light emitting device includes the aforementioned
fluoride fluorescent material and a light source having a light
emission peak in a range of 380 nm or more and 485 nm or less. The
light emitting device may further include other constitutional
members depending on necessity. The light emitting device includes
the fluoride fluorescent material that emits light having a high
light emission intensity and a good chromatic purity with a small
full width at half maximum of the light emission spectrum with the
light emitted from the excitation light source, and thereby can
reproduce a wide range of colors in the chromaticity coordinates
and can emit mixed light excellent in color reproducibility.
Light Source
[0033] The light source for exciting the fluoride fluorescent
material (which may be hereinafter referred to as an "excitation
light source") preferably has a light emission peak wavelength in a
range of 420 nm or more and 485 nm or less, and more preferably has
a light emission peak wavelength in a range of 440 nm or more and
480 nm or less, for efficiently exciting the fluoride fluorescent
material to use effectively the visible light. The excitation light
source used is preferably a semiconductor light emitting element
(which may be hereinafter referred to as a "light emitting
element"). The use of a semiconductor light emitting element such
as a LED or a LD as the excitation light source may provide a light
emitting device that has high efficiency, high linearity of output
with respect to input, and high stability against mechanical
impacts. The semiconductor light emitting element used may be, for
example, a semiconductor light emitting element using a nitride
semiconductor (In.sub.XAl.sub.YGa.sub.1-X-YN, wherein 0.ltoreq.X,
0.ltoreq.Y, X+Y.ltoreq.1). The full width at half maximum of the
light emission peak in the light emission spectrum of the light
emitting element is preferably, for example, 30 nm or less.
Fluorescent Material
[0034] In the light emitting device, the aforementioned fluoride
fluorescent material may be contained, for example, in a
fluorescent member that covers the excitation light source. In the
light emitting device having the excitation light source covered
with the fluorescent member containing the fluoride fluorescent
material, a part of the light emitted from the excitation light
source is absorbed by the fluoride fluorescent material, and
emitted therefrom as red light.
[0035] The light emitting device may include an additional
fluorescent material other than the fluoride fluorescent material,
in addition to the fluoride fluorescent material. The additional
fluorescent material other than the fluoride fluorescent material
suffices to be one that absorbs the light from the light source and
subjects the light to wavelength conversion to light having a
wavelength different from the fluoride fluorescent material. It is
preferred that the light emitting device further includes a
fluorescent material having a light emission peak wavelength in a
range of 495 nm or more and 573 nm or less.
[0036] The additional fluorescent material other than the fluoride
fluorescent material is preferably, for example, at least one kind
selected from the group consisting of a rare earth aluminate
fluorescent material, a halogen silicate fluorescent material, an
alkaline earth aluminate fluorescent material, a .beta.-SiAlON
fluorescent material, an alkaline earth metal silicate fluorescent
material, and an alkaline earth sulfide fluorescent material, which
are activated mainly with a lanthanoid element, such as Ce, an
alkaline earth metal halophosphate fluorescent material and a
germanate salt fluorescent material, which are activated mainly
with a lanthanoid element, such as Eu, or a transition metal
element, such as Mn, a nitride fluorescent material, an oxynitride
fluorescent material, an alkaline earth metal borohalide
fluorescent material, an alkaline earth metal aluminate fluorescent
material, an alkaline earth silicon nitride fluorescent material
and a rare earth silicate fluorescent material, which are activated
mainly with a lanthanoid element, such as Eu and Ce, and an organic
or organic complex fluorescent material, which is activated mainly
with a lanthanoid element, such as Eu.
[0037] Examples of the fluorescent material having a light emission
peak wavelength in a range of 495 nm or more and 573 nm or less by
irradiation with an excitation light source having a light emission
peak wavelength in a range of 380 nm or more and 485 nm or less
include (Lu,Y,Gd,Lu).sub.3(Ga,Al).sub.5O.sub.12:Ce, (Ca, Sr,
Ba).sub.8MgSi.sub.4O.sub.16(F, Cl,Br).sub.2:Eu,
Si.sub.6-zAl.sub.zO.sub.zN.sub.8-z:Eu (0<z.ltoreq.4.2), and
(Ca,Sr,Ba).sub.2SiO.sub.4:Eu. In the formulae showing the
compositions of the fluorescent materials, the plural elements
delimited by a comma (,) means that at least one kind of the plural
elements is contained in the composition. In the description
herein, in the formulae showing the compositions of the fluorescent
materials, the term before the colon (:) shows the elements
constituting the base crystal and the molar ratios thereof, and the
term after the colon (:) shows the activation element.
[0038] An example of the light emitting device will be described
with reference to the drawing. FIG. 1 is a schematic cross
sectional view showing an example of the light emitting device. The
light emitting device is an example of a surface mounted light
emitting device.
[0039] The light emitting device 100 has a light emitting element
10 that emits light having a light emission peak wavelength on the
short wavelength side of the visible light, for example, in a range
of 380 nm or more and 485 nm or less, and a molded body 40 having
the light emitting element 10 disposed thereon. The molded body 40
has a first lead 20 and a second lead 30, which are integrally
molded with a thermoplastic resin or a thermosetting resin. The
molded body 40 has a concave portion having a bottom surface and a
side surface, and the light emitting element 10 is disposed on the
bottom surface of the concave portion. The light emitting element
10 has one pair of positive and negative electrodes, and the one
pair of positive and negative electrodes are electrically connected
to the first lead 20 and the second lead 30 respectively with wires
60. The light emitting element 10 is sealed with a fluorescent
member 50. The fluorescent member 50 contains a fluorescent
material 70 containing a fluoride fluorescent material performing
wavelength conversion of the light emitted from the light emitting
element 10. The fluorescent material 70 contains the fluoride
fluorescent material as a first fluorescent material 71, and may
contain a second fluorescent material 72 that emits light having a
light emission peak wavelength in a wavelength range different from
the fluoride fluorescent material with the excitation light from
the light emitting element 10.
[0040] The fluorescent member may contain a resin and the
fluorescent material, and examples of the resin include a silicone
resin and an epoxy resin. The fluorescent member may further
contain a light diffusion material, such as silica, titanium oxide,
zinc oxide, zirconium oxide, and alumina, in addition to the resin
and the fluorescent material. The light diffusing material
contained may reduce the directionality from the light emitting
element to enhance the viewing angle.
Method for Producing Fluoride Fluorescent Material
[0041] The method for producing a fluoride fluorescent material,
includes: preparing fluoride particles including a composition
including K, Ge, Mn.sup.4+, and F, and having a molar ratio of K of
2, a total molar ratio of Ge and Mn.sup.4+ of 1, a molar ratio of
Mn.sup.4+ of more than 0 and less than 0.2, and a molar ratio of F
of 6 in 1 mol of the composition; and bringing the fluoride
particles into contact with a fluorine-containing substance, and
subjecting to a heat treatment at a temperature of 400.degree. C.
or more. The fluoride particles are brought into contact with the
fluorine-containing substance and are subjected to a heat treatment
at a temperature of 400.degree. C. or more, the amount (molar
ratio) of fluorine in the fluoride particles it self does not
change, but the crystal structure thereof changes. Specifically,
the crystal structure of the fluoride particles changes from the
crystal structure of K.sub.2GeF.sub.6 to the structure close to the
crystal structure of K.sub.2MnF.sub.6.
[0042] The fluoride particles preferably have a composition
represented by the following formula (I):
K.sub.2[Ge.sub.1-aMn.sup.4+.sub.aF.sub.6] (I)
[0043] wherein in the formula (I), a satisfies 0<a<0.2.
[0044] The fluoride particles are brought into contact with a
fluorine-containing substance and subjected to a heat treatment at
a temperature of 400.degree. C. or more, and thereby a fluoride
fluorescent material having a crystal structure having been changed
from the K.sub.2GeF.sub.6 crystal structure to a crystal structure
similar to the K.sub.2MnF.sub.6 crystal structure is obtained. The
fluoride fluorescent material has a light emission spectrum having
a first light emission peak in a range of 615 nm or more and less
than 625 nm having a full width at half maximum of 6 nm or less,
and a second light emission peak in a range of 625 nm or more and
less than 635 nm, and thus the first light emission peak has a
small full width at half maximum. Accordingly, a good chromatic
purity is obtained, and a higher light emission intensity is
obtained due to the first light emission peak and the second light
emission peak.
Method for Producing Fluoride Particles
[0045] The fluoride particles may be produced, for example, by a
production method including a step of mixing a first solution
containing at least potassium ion and hydrogen fluoride, a second
solution containing at least a first complex ion including
tetravalent manganese and hydrogen fluoride, and a third solution
containing at least a second complex ion including germanium and
fluoride ion. The first solution, the second solution, and the
third solution are mixed, and thereby fluoride particles that have
a target composition and function as a fluorescent material can be
produced by a simple method excellent in productivity.
First Solution
[0046] The first solution (which may be hereinafter referred to as
a "solution A") contains at least potassium ion and hydrogen
fluoride, and may further contain additional components depending
on necessity. The first solution may be, for example, an aqueous
solution of hydrofluoric acid containing potassium ion. The first
solution may be obtained by dissolving a compound containing
potassium in an aqueous solution of hydrofluoric acid. Examples of
the compound containing potassium used in the first solution
include a water soluble compound, such as a halide, a
hydrofluoride, a hydroxide, an acetate, and a carbonate. Specific
examples thereof include water soluble potassium salts, such as KF,
KHF.sub.2, KOH, KCl, KBr, KI, potassium acetate, and
K.sub.2CO.sub.3. Among these, KHF.sub.2 is preferred since this
compound may be dissolved in the solution without decrease of the
hydrogen fluoride concentration thereof and has a small heat of
dissolution and high safety. The compound containing potassium
constituting the first solution may be used alone or as a
combination of two or more kinds thereof.
[0047] The hydrogen fluoride concentration in the first solution is
generally 1% by mass or more, preferably 3% by mass or more, and
more preferably 5% by mass or more. The hydrogen fluoride
concentration in the first solution is generally 80% by mass or
less, preferably 75% by mass or less, and more preferably 70% by
mass or less.
[0048] The potassium ion concentration in the first solution is
generally 1% by mass or more, preferably 3% by mass or more, and
more preferably 5% by mass or more. The potassium ion concentration
in the first solution is generally 30% by mass or less, preferably
25% by mass or less, and more preferably 20% by mass or less. In
the case where the potassium ion concentration is 5% by mass or
more, there may be a tendency that the yield of the fluoride
particles is increased.
Second Solution
[0049] The second solution (which may be hereinafter referred to as
a "solution B") contains a first complex ion including tetravalent
manganese and hydrogen fluoride, and may further contain additional
components depending on necessity. The second solution may be, for
example, an aqueous solution of hydrofluoric acid in which a
tetravalent manganese source is dissolved. The manganese source is
a compound containing tetravalent manganese. Specific examples of
the manganese source contained in the second solution include
K.sub.2MnF.sub.6, KMnO.sub.4, and K.sub.2MnCl.sub.6. Among these,
K.sub.2MnF.sub.6 is preferred since this compound does not contain
chlorine, which tends to destabilize the crystal lattice through
distortion, and can stably exist in hydrofluoric acid as MnF.sub.6
complex ion while retaining the oxidation number (tetravalent)
capable of performing the activation. A manganese source containing
potassium may also function as the source of potassium contained in
the first solution. The manganese source constituting the second
solution may be used alone or as a combination of two or more kinds
thereof.
[0050] The hydrogen fluoride concentration in the second solution
is generally 1% by mass or more, preferably 3% by mass or more, and
more preferably 5% by mass or more. The hydrogen fluoride
concentration in the second solution is generally 80% by mass or
less, preferably 75% by mass or less, and more preferably 70% by
mass or less.
[0051] The first complex ion concentration in the second solution
is generally 0.01% by mass or more, preferably 0.03% by mass or
more, and more preferably 0.05% by mass or more. The first complex
ion concentration in the second solution is generally 5% by mass or
less, preferably 4% by mass or less, and more preferably 3% by mass
or less.
Third Solution
[0052] The third solution (which may be hereinafter referred to as
a "solution C") contains a second complex ion including germanium
and fluoride ion, and may further contain additional components
depending on necessity. The third solution may be, for example, an
aqueous solution in which a second complex ion source is
dissolved.
[0053] The second complex ion source is preferably a compound that
contains germanium and fluoride ion and is excellent in solubility
in the solution. Specific examples of the second complex ion source
include H.sub.2GeF.sub.6, Na.sub.2GeF.sub.6,
(NH.sub.4).sub.2GeF.sub.6, Rb.sub.2GeF.sub.6, and
Cs.sub.2GeF.sub.6. Among these, H.sub.2GeF.sub.6 is preferred since
this compound has high solubility in water and does not contain an
alkali metal element as an impurity. The second complex ion source
constituting the third solution may be used alone or as a
combination of two or more kinds thereof.
[0054] The second complex ion concentration in the third solution
is generally 10% by mass or more, preferably 15% by mass or more,
and more preferably 20% by mass or more. The second complex ion
concentration in the third solution is generally 60% by mass or
less, preferably 55% by mass or less, and more preferably 50% by
mass or less.
[0055] As the mixing method of the first solution, the second
solution, and the third solution, for example, the second solution
and the third solution may be added and mixed into the first
solution under stirring, or the first solution and the second
solution may be added and mixed into the third solution under
stirring. Alternatively, the first solution, the second solution,
and the third solution each may be placed in a vessel and then
mixed by stirring.
[0056] By mixing the first solution, the second solution, and the
third solution, the first complex ion, potassium ion, and the
second complex ion are reacted with each other to deposit the
target fluoride particles. The deposited crystals may be recovered
through solid-liquid separation by filtration. The crystals may be
rinsed with a solvent, such as ethanol, isopropyl alcohol, water,
and acetone. The crystals may be subjected to a drying treatment,
and may be dried at generally 50.degree. C. or more, preferably
55.degree. C. or more, and more preferably 60.degree. C. or more,
and may be dried at generally 110.degree. C. or less, preferably
105.degree. C. or less, and more preferably 100.degree. C. or less.
The drying time may just be time which can evaporated water
attached to the fluoride particles. The drying time is preferably
in a range of 3 hours or more and 20 hours or less, more preferably
in a range of 5 hours or more and 15 hours or less. The drying time
may be, for example, approximately 10 hours.
[0057] In mixing the first solution, the second solution, and the
third solution, the mixing ratio of the first solution, the second
solution, and the third solution is preferably appropriately
controlled to provide the fluoride particles as a product having
the target composition, in consideration of the discrepancy between
the composition during preparation of the aforementioned raw
materials of the fluorescent material and the composition of the
resulting fluoride particles.
Rinsing
[0058] The resulting fluoride particles may be rinsed with a
rinsing liquid for removing impurities. Examples of the rinsing
liquid include ethanol, isopropyl alcohol, water, and acetone.
Among these, water having high solubility to fluoride salts, such
as potassium fluoride, is preferably used. The water used is
preferably deionized water. The rinsing liquid may contain a
reducing agent, such as hydrogen peroxide. In the case where the
rinsing liquid contains a reducing agent, even though manganese as
an activating agent in the fluoride particles is oxidized by the
heat treatment, the oxidized manganese is reduced with the reducing
agent in the rinsing liquid, so as to enhance the light emission
characteristics of the resulting fluoride fluorescent material. The
fluoride fluorescent material after rinsing may be further
subjected to a drying treatment, and the drying temperature in the
drying treatment is generally 50.degree. C. or more, preferably
55.degree. C. or more, and more preferably 60.degree. C. or more,
and is generally 110.degree. C. or less, preferably 105.degree. C.
or less, and more preferably 100.degree. C. or less. The drying
time may just be time which can evaporated water attached to the
fluoride fluorescent material. The drying time is preferably in a
range of 3 hours or more and 20 hours or less, more preferably in a
range of 5 hours or more and 15 hours or less. The drying time may
be, for example, approximately 10 hours.
Heat Treatment of Fluoride Particles
[0059] The fluoride particles are brought into contact with a
fluorine-containing substance and subjected to a heat treatment at
a temperature of 400.degree. C. or more, and thereby the crystal
structure around Mn.sup.4+ as the activation element in the
fluoride particles is stabilized, so as to provide the fluoride
fluorescent material, in which the crystal structure having a
composition shown by K.sub.2GeF.sub.6 of the fluoride particles has
been changed to a crystal structure similar to the crystal
structure having a composition shown by K.sub.2MnF.sub.6. The
fluoride particles are changed to a stable crystal structure by
bringing into contact with a fluorine-containing substance and
subjecting to a heat treatment at a temperature of 400.degree. C.
or more. The light emission spectrum of the fluoride fluorescent
material obtained through the heat treatment has a first light
emission peak in a range of 615 nm or more and less than 625 nm
having a full width at half maximum of 6 nm or less, and a second
light emission peak in a range of 625 nm or more and less than 635
nm. The resulting fluoride fluorescent material preferably has an
internal quantum efficiency under excitation of light having a
wavelength of 450 nm of 85% or more. The resulting fluoride
fluorescent material preferably has a composition represented by
the aforementioned formula (I).
[0060] The resulting fluoride fluorescent material preferably has a
light emission intensity of 30% or more at the first light emission
peak in a range of 615 nm or more and less than 625 nm based on the
light emission intensity at the second light emission peak in a
range of 625 nm or more and less than 635 nm as 100%. For example,
in the case where the fluoride particles contain K, Ge, Si,
Mn.sup.4+, and F in the composition thereof, a distorted crystal
structure is formed since in Ge and Si constituting the skeleton of
the crystal structure, the ionic radius of Si is considerably
smaller than the ionic radius of Ge or the ionic radius of
Mn.sup.4+ as the activation element. Furthermore, in the case where
the fluoride particles contain K, Ge, Si, Mn.sup.4+, and F in the
composition thereof, even though the fluoride particles have a
crystal structure similar to the K.sub.2MnF.sub.6 crystal
structure, the crystal structure is changed to a crystal structure
similar to the K.sub.2SiF.sub.6 crystal structure by the heat
treatment at a temperature of 400.degree. C. or more, and the
resulting fluoride fluorescent material has a light emission
spectrum, in which the first light emission peak in a range of 615
nm or more and less than 625 nm has a lowered light emission
intensity.
[0061] The temperature of the heat treatment of the fluoride
particles is preferably a temperature exceeding 400.degree. C.,
more preferably 425.degree. C. or more, and further preferably
450.degree. C. or more. In the case where the temperature of the
heat treatment of the fluoride particles is less than 400.degree.
C., the fluoride particles undergo small change of the crystal
structure, and it is difficult to achieve a higher light emission
intensity. In the case where the temperature of the heat treatment
of the fluoride particles is too high, the fluoride particles may
be decomposed in some cases. Accordingly, the temperature of the
heat treatment of the fluoride particles is preferably 600.degree.
C. or less, and more preferably in a range of 450.degree. C. or
more and 550.degree. C. or less.
[0062] The heat treatment of the fluoride particles is preferably
performed in an inert gas atmosphere. The inert gas atmosphere
herein means an atmosphere containing argon, helium, nitrogen as a
major component in the atmosphere. The major component in the
atmosphere means that at least one kind of gas selected from argon,
helium, and nitrogen has a gas concentration of 70% by volume or
more in the atmosphere. The inert gas atmosphere preferably
contains nitrogen. The nitrogen gas concentration in the inert gas
atmosphere is preferably 70% by volume or more, more preferably 80%
by volume or more, further preferably 85% by volume or more, and
still further preferably 90% by volume or more. The inert gas
atmosphere may contain oxygen as an unavoidable impurity. Herein,
an atmosphere that has a concentration of oxygen contained in the
atmosphere of 15% by volume or less may be designated as the inert
gas atmosphere. The concentration of oxygen in the inert gas
atmosphere is preferably 0.3% by volume or less, and more
preferably 0.1% by volume or less, and it is further preferred that
no oxygen is contained in the atmosphere. In the case where the
oxygen concentration in the inert gas atmosphere in the heat
treatment of the fluoride particles is the prescribed value or
more, Mn.sup.4+ as the activation element in the fluoride particles
may be oxidized to lower the light emission intensity of the
fluoride fluorescent material.
[0063] The fluorine-containing substance is preferably at least one
kind selected from the group consisting of F.sub.2, CHF.sub.3,
CF.sub.4, NH.sub.4HF.sub.2, NH.sub.4F, SiF.sub.4, and NF.sub.3
since these compounds can be readily brought into contact with the
fluoride particles. The fluorine-containing substance is more
preferably F.sub.2 or NH.sub.4F.
[0064] The temperature of the environment, in which the fluoride
particles are brought into contact with the fluorine-containing
substance in a solid state or a liquid state, may be from room
temperature (20.degree. C..+-.5.degree. C.) to a temperature lower
than the heat treatment temperature, and may be the heat treatment
temperature. Specifically, the temperature may be a low temperature
of 20.degree. C. or more and less than 400.degree. C., and may be
the heat treatment temperature of 400.degree. C. or more. In the
case where the temperature of the environment, in which the
fluoride particles are brought into contact with the
fluorine-containing substance in a solid state at ordinary
temperature, is 20.degree. C. or more and less than 400.degree. C.,
the fluoride particles are brought into contact with the
fluorine-containing substance and then subjected to the heat
treatment at 400.degree. C. or more.
[0065] In the case where the fluorine-containing substance is in a
solid state or a liquid state at ordinary temperature, it is
preferred that the fluorine-containing substance in an amount of 1%
by mass or more and 20% by mass or less in terms of fluorine
element amount based on the total amount of the fluoride particles
and the fluorine-containing substance as 100% by mass is brought
into contact with the fluoride particles. The fluoride particles
are brought into contact with the fluorine-containing substance,
and thereby the fluoride fluorescent material having a high light
emission intensity can be provided.
[0066] In the case where the fluorine-containing substance is a
gas, or a gas containing fluorine generated from a
fluorine-containing substance in a solid state or a liquid state,
the fluoride particles may be brought into contact therewith by
disposing the fluoride particles in an inert gas atmosphere
containing the fluorine-containing substance. It is also possible
that the fluoride particles are disposed in an inert gas atmosphere
containing the fluorine-containing substance, and then the fluoride
particles are subjected to the heat treatment at a temperature of
400.degree. C. or more in the inert gas atmosphere containing the
fluorine-containing substance. In the case where the
fluorine-containing substance is F.sub.2 (fluorine gas), and the
fluoride particles are subjected to the heat treatment at a
temperature of 400.degree. C. or more in an inert gas atmosphere
containing F.sub.2, the F.sub.2 concentration of the inert gas
atmosphere is preferably 3% by volume or more, and more preferably
5% by volume or more, and is preferably 30% by volume or less, and
more preferably 25% by volume or less. In the case where the
concentration of fluorine gas in the inert gas atmosphere is 3% by
volume or more and 30% by volume or less, the portion of the
fluoride particles deficient in fluorine as a result of the heat
treatment is compensated with fluorine, so as to stabilize the
crystal structure, and thereby the fluoride fluorescent material
having a high light emission intensity can be obtained.
[0067] The retention time in the heat treatment of the fluoride
particles means a period of time where the fluoride particles are
subjected to the heat treatment at the temperature of the heat
treatment. The retention time in the heat treatment is preferably
in a range of 2 hours or more and 20 hours or less, and more
preferably in a range of 4 hours or more and 15 hours or less. In
the case where the retention time of the heat treatment at a
temperature of 400.degree. C. or more is in a range of 2 hours or
more and 20 hours or less, the crystal structure is stabilized, and
thereby the fluoride fluorescent material having a high light
emission intensity can be obtained.
[0068] The pressure in the heat treatment may be the atmospheric
pressure (0.101 MPa) or a pressurized atmosphere of more than 0.101
MPa and 1 MPa or less.
EXAMPLES
[0069] The present disclosure will be described more specifically
with reference to examples below. The present disclosure is not
limited to the examples.
Example 1
Production of Fluoride Particles
[0070] The production method of fluoride particles will be
described. 1,483.7 g of KHF.sub.2 was weighed, and the KHF.sub.2
was dissolved in 5.0 L of an 11% by mass HF aqueous solution, so as
to prepare a solution A (first solution). 123.56 g of
K.sub.2MnF.sub.6 was weighed, and the K.sub.2MnF.sub.6 was
dissolved in 5.0 L of a 55% by mass HF aqueous solution, and 5.0 L
of deionized water was added thereto, so as to prepare a solution B
(second solution). 993.56 g of GeO.sub.2 was weighed, and the
GeO.sub.2 was dissolved in a 55% by mass HF aqueous solution to
prepare 4,480 g of an aqueous solution containing 40% by mass of
H.sub.2GeF.sub.6, which was designated as a solution C (third
solution).
[0071] Subsequently, the solution A was stirred at room
temperature, to which the solution B and the solution C each were
added dropwise over approximately 10 minutes to provide a
precipitate.
[0072] The resulting precipitate was subjected to solid-liquid
separation and then ethanol rinsing, and was dried at 90.degree. C.
for 10 hours to produce fluoride particles.
Heat Treatment of Fluoride Particles
[0073] The resulting fluoride particles were subjected to a heat
treatment in an atmosphere containing fluorine gas (F.sub.2) and
nitrogen gas (N.sub.2) as an inert gas, having a fluorine gas
concentration of 20% by volume and a nitrogen gas concentration of
80% by volume, at a temperature of 450.degree. C. for a retention
time of 8 hours, and thereby a fluoride fluorescent material of
Example 1 having a composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained.
Example 2
[0074] A fluoride fluorescent material of Example 2 having a
composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained in the
same manner as in Example 1 except that the heat treatment
temperature was changed to 500.degree. C.
Example 3
[0075] A fluoride fluorescent material of Example 3 having a
composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained in the
same manner as in Example 1 except that the heat treatment
temperature was changed to 550.degree. C.
Example 4
[0076] A fluoride fluorescent material of Example 4 having a
composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained in the
same manner as in Example 1 except that the heat treatment
temperature was changed to 400.degree. C.
Comparative Example 1
[0077] The fluoride particles produced in Example 1 were designated
as a fluoride fluorescent material of Comparative Example 1 having
a composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] without a heat
treatment.
Comparative Example 2
[0078] A fluoride fluorescent material of Comparative Example 2
having a composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained in the
same manner as in Example 1 except that the heat treatment
temperature was changed to 300.degree. C.
Comparative Example 3
[0079] A fluoride fluorescent material of Comparative Example 3
having a composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained in the
same manner as in Example 1 except that the heat treatment
temperature was changed to 150.degree. C.
Comparative Example 4
[0080] A fluoride fluorescent material of Comparative Example 4
having a composition represented by
K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] was obtained in the
same manner as in Example 1 except that the heat treatment
temperature was changed to 500.degree. C., and the fluoride
particles were subjected to the heat treatment in an inert gas
atmosphere having a nitrogen gas concentration of 100% by volume
without contact with a fluorine-containing substance.
Comparative Example 5
[0081] 478.9 g of KHF.sub.2 was weighed, and the KHF.sub.2 was
dissolved in 5.0 L of a 55% by mass HF aqueous solution, so as to
prepare a solution A (first solution). 65.9 g of K.sub.2MnF.sub.6
was weighed, and the K.sub.2MnF.sub.6 was dissolved in 1.8 L of a
55% by mass HF aqueous solution, so as to prepare a solution B
(second solution). 224.5 g of GeO.sub.2 was weighed, and the
GeO.sub.2 was dissolved in a 55% by mass HF aqueous solution, and
1,012 g of an aqueous solution containing 40% by mass of
H.sub.2GeF.sub.6 and 331 g of a 40% by mass H.sub.2SiF.sub.6
aqueous solution were mixed, so as to prepare a solution C (third
solution).
[0082] Subsequently, the solution A was stirred at room
temperature, to which the solution B and the solution C each were
added dropwise over approximately 10 minutes to provide a
precipitate. The resulting precipitate was subjected to
solid-liquid separation and then ethanol rinsing, and was dried at
90.degree. C. for 10 hours to produce fluoride particles. The
resulting fluoride particles were designated as a fluoride
fluorescent material of Comparative Example 5 having a composition
represented by
K.sub.2[Si.sub.0.54Ge.sub.0.41Mn.sup.4+.sub.0.05F.sub.6] without
subjecting to a heat treatment.
Comparative Example 6
[0083] The fluoride particles obtained in Comparative Example 5
were subjected to a heat treatment in an atmosphere containing
fluorine gas (F.sub.2) and nitrogen gas (N.sub.2) as an inert gas,
having a fluorine gas concentration of 20% by volume and a nitrogen
gas concentration of 80% by volume, at a temperature of 450.degree.
C. for a retention time of 8 hours, and thereby a fluoride
fluorescent material of Comparative Example 6 having a composition
represented by
K.sub.2[Si.sub.0.54Ge.sub.0.41Mn.sup.4+.sub.0.05F.sub.6] was
obtained.
Reference Example 1
[0084] As Reference Example 1, a fluoride fluorescent material
having a composition represented by K.sub.2SiF.sub.6:Mn.sup.4+ was
prepared.
Reference Example 2
[0085] The fluoride fluorescent material of Reference Example 1
having a composition represented by K.sub.2SiF.sub.6:Mn.sup.4+ was
subjected to a heat treatment under the same condition as in
Example 1, so as to provide a fluoride fluorescent material of
Reference Example 2.
Evaluation
Light Emission Spectrum
[0086] The resulting fluoride fluorescent materials of Examples and
Comparative Examples each were irradiated with excitation light
having a light emission peak wavelength of 450 nm with a Quantum
Efficiency Measurement System (QE-2000, manufactured by Otsuka
Electronics Co., Ltd.), and the light emission spectra of the
fluoride fluorescent materials at room temperature were measured.
FIG. 2 shows the light emission spectrum of the fluoride
fluorescent material of Example 1. FIG. 3 shows the light emission
spectrum of the fluoride fluorescent material of Comparative
Example 1. FIG. 6 shows the light emission spectrum of the fluoride
fluorescent material of Reference Example 1 having a composition
represented by K.sub.2SiF.sub.6:Mn.sup.4+. FIG. 7 shows the light
emission spectrum of the fluoride fluorescent material of Reference
Example 2 having a composition represented by
K.sub.2SiF.sub.6:Mn.sup.4+.
Chromaticities x,y
[0087] From the data of each of the light emission spectra measured
for the fluoride fluorescent materials of Examples and Comparative
Examples, the chromaticity x and the chromaticity y in the xy
chromaticity coordinates in the CIE (Commission International de
l'eclarirage) 1931 color coordinate system were obtained. The
results are shown in Table 1.
Relative Light Emission Intensity
[0088] From the data of each of the light emission spectra measured
for the fluoride fluorescent materials of Examples and Comparative
Examples, the maximum light emission intensity of each of the
fluoride fluorescent materials of Examples 1 to 4 and Comparative
Examples 2 to 6 was obtained as a relative light emission intensity
with respect to the maximum light emission intensity in the light
emission spectrum of the fluoride fluorescent material of
Comparative Example 1 as 100%. The results are shown in Table
1.
Full Width at Half Maximum
[0089] From the data of each of the light emission spectra measured
for the fluoride fluorescent materials of Examples and Comparative
Examples, the full width at half maximum of the first light
emission peak in a range of 615 nm or more and less than 625 nm was
obtained. The results are shown in Table 1.
Internal Quantum Efficiency
[0090] From the data of each of the light emission spectra measured
for the fluoride fluorescent materials of Examples and Comparative
Examples, the internal quantum efficiency (%) under excitation of
light having a wavelength of 450 nm was obtained. The results are
shown in Table 1. The light emission spectra data of each of the
fluorescent material of Examples and Comparative Examples ware
measured at room temperature using Quantum Efficiency Measurement
System (QE-2000, manufactured by Otsuka Electronics Co., Ltd.). The
internal quantum efficiency is obtained by the following
equation;
Internal Quantum Efficiency=emitted light quantum number/absorbed
light quantum number
Light Emission Peak Intensity Ratio
[0091] From the data of each of the light emission spectra measured
for the fluoride fluorescent materials of Examples and Comparative
Examples, the light emission peak intensity ratio of the first
light emission peak in a range of 615 nm or more and less than 625
nm with respect to the light emission intensity at the second light
emission peak in a range of 625 nm or more and less than 635 nm as
100% was obtained. The results are shown in Table 1.
X-ray Diffraction Pattern
[0092] X-ray diffraction patterns of the fluoride fluorescent
materials of Example 1 and Comparative Example 1 each were measured
with a horizontal sample multipurpose X-ray diffraction system
(Ultima IV, manufactured by Rigaku Corporation, X-ray source:
CuK.alpha. line (.lamda.=1.5418 .ANG., tube voltage: 40 kV tube
current: 40 mA)). FIG. 4 shows X-ray diffraction patterns of the
fluoride fluorescent materials of Example 1 and Comparative Example
1. FIG. 5 shows an X-ray diffraction pattern of the fluoride
fluorescent material of Example 1 and an X-ray diffraction pattern
of the crystal structure model of K.sub.2MnF.sub.6 according to
ICDD Card No. 01-077-2133 using the ICDD (International Center for
Diffraction Data) database. FIG. 8 shows X-ray diffraction patterns
of the fluoride fluorescent materials of Reference Example 1 and
Reference Example 2 each having a composition represented by
K.sub.2SiF.sub.6:Mn.sup.4+.
TABLE-US-00001 TABLE 1 Light emission characteristics Full width at
Relative light half maximum Internal Light emission Heat treatment
condition emission of first light quantum peak intensity
Temperature Chromaticity intensity emission peak efficiency ratio
(.degree. C.) Atmosphere x y (%) (nm) (%) (%) Example 1 450
F.sub.2/N.sub.2 0.694 0.306 132.9 4.4 98.5 45 Example 2 500
F.sub.2/N.sub.2 0.694 0.306 125.5 4.7 97.4 37 Example 3 550
F.sub.2/N.sub.2 0.694 0.306 131.0 4.4 98.6 43 Example 4 400
F.sub.2/N.sub.2 0.693 0.307 114.7 4.4 86.0 44 Comparative -- --
0.694 0.305 100.0 -- 81.6 11 Example 1 Comparative 300
F.sub.2/N.sub.2 0.693 0.307 76.4 4.5 56.2 39 Example 2 Comparative
150 F.sub.2/N.sub.2 0.695 0.305 98.1 -- 77.8 11 Example 3
Comparative 500 N.sub.2 0.691 0.308 48.9 4.3 35.9 48 Example 4
Comparative -- -- 0.693 0.307 103.5 4.4 84.8 47 Example 5
Comparative 450 F.sub.2/N.sub.2 0.693 0.306 106.8 -- 83.8 24
Example 6
[0093] As shown in Table 1, the fluoride fluorescent materials of
Examples 1 to 4 each had a higher relative light emission intensity
than the fluoride fluorescent material of Comparative Example 1 and
had a high internal quantum efficiency of 85% or more. In
particular, the fluoride fluorescent materials of Examples 1 to 3
each had an internal quantum efficiency of 90% or more. The
fluoride fluorescent materials of Examples 1 to 4 each have a high
light emission intensity with an internal quantum efficiency under
excitation of light having a wavelength of 450 nm of 85% or more
since the light emission spectrum thereof has the second light
emission peak in a range of 625 nm or more and less than 635 nm and
the first light emission peak having a full width at half maximum
of 6 nm or less and a light emission intensity of 30% or more based
on the light emission intensity at the second light emission peak
as 100% in a range of 615 nm or more and less than 625 nm.
[0094] The fluoride fluorescent material of Comparative Example 1
had no light emission peak in a range of 615 nm or more and less
than 625 nm, and the light emission intensity at the light emission
peak in a range of 615 nm or more and less than 625 nm was less
than 30% based on the light emission intensity at the light
emission peak in a range of 625 nm or more and less than 635 nm as
100%.
[0095] The fluoride fluorescent material of Comparative Example 2
suffered relatively small influence of the heat treatment since the
temperature of the heat treatment in an inert gas atmosphere was
less than 400.degree. C. Accordingly, the fluoride fluorescent
material had a light emission peak in a range of 615 nm or more and
less than 625 nm, but had a light emission intensity that was not
enhanced but was lower than the fluoride fluorescent material of
Comparative Example 1, and a low internal quantum efficiency.
[0096] The fluoride fluorescent material of Comparative Example 3
suffered relatively small influence of the heat treatment since the
temperature of the heat treatment in an inert gas atmosphere was as
low as 150.degree. C., and had no light emission peak in a range of
615 nm or more and less than 625 nm. Accordingly, the light
emission intensity thereof was lower than the fluoride fluorescent
material of Comparative Example 1, and the internal quantum
efficiency thereof was lowered.
[0097] The fluoride fluorescent material of Comparative Example 4
was subjected to the heat treatment without contact with a
fluorine-containing substance, and therefore fluorine was not
supplied to the composition of the fluoride fluorescent material.
Accordingly, the light emission intensity thereof was lower than
the fluoride fluorescent material of Comparative Example 1, and the
internal quantum efficiency thereof was lowered.
[0098] The fluoride fluorescent material of Comparative Example 5
had a relative light emission intensity that was slightly higher
than the fluoride fluorescent material of Comparative Example 1,
and the light emission spectrum thereof had the first light
emission peak in a range of 615 nm or more and less than 625 nm
having a full width at half maximum of 6 nm or less. However, the
crystal structure was distorted due to Si contained in the
composition, and thereby the light emission intensity at the first
light emission peak was small, and the internal quantum efficiency
under excitation of light having a wavelength of 450 nm did not
reach 85%.
[0099] The fluoride fluorescent material of Comparative Example 6
had a relative light emission intensity that was higher than the
fluoride fluorescent material of Comparative Example 1, but the
light emission intensity at the light emission peak in a range of
615 nm or more and less than 625 nm was small, and the internal
quantum efficiency under excitation of light having a wavelength of
450 nm was lowered. It is estimated that the fluoride fluorescent
material of Comparative Example 6 has a distorted crystal structure
due to Si contained in the composition. By subjecting the fluoride
particles having the distorted crystal structure to the heat
treatment at a temperature of 400.degree. C., the crystal structure
is changed from a crystal structure similar to the K.sub.2MnF.sub.6
crystal structure to a crystal structure similar to the
K.sub.2SiF.sub.6 crystal structure. It is estimated that in the
light emission spectrum, consequently, the light emission intensity
at the light emission peak in a range of 615 nm or more and less
than 625 nm is decreased.
[0100] As shown in FIG. 2, the fluoride fluorescent material of
Example 1 had the light emission spectrum having the first light
emission peak in a range of 615 nm or more and less than 625 nm
having a full width at half maximum of 6 nm or less, and the second
light emission peak in a range of 625 nm or more and less than 635
nm. As shown in FIG. 3, on the other hand, the fluoride fluorescent
material of Comparative Example 1 had the light emission peak in a
range of 625 nm or more and less than 635 nm, but had no light
emission peak in a range of 615 nm or more and less than 625 nm. It
was confirmed from the results that the fluoride fluorescent
material of Example 1 had the changed crystal structure, which was
different from the fluoride fluorescent material having no first
light emission peak in a range of 615 nm or more and less than 625
nm.
[0101] As shown in FIG. 4, the X-ray diffraction pattern of the
fluoride fluorescent material of Example 1 having a composition
represented by K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] had
peaks at the positions in diffraction angle 20 that were different
from the X-ray diffraction pattern of the fluoride fluorescent
material of Comparative Example 1 having a composition represented
by K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6], from which it was
confirmed that the fluoride fluorescent material of Example 1 had
the changed crystal structure, which was different from the
fluoride fluorescent material of Comparative Example 1. The
fluoride fluorescent material of Comparative Example 1 had a
K.sub.2GeF.sub.6 crystal structure.
[0102] As shown in FIG. 5, the X-ray diffraction pattern of the
fluoride fluorescent material of Example 1 having a composition
represented by K.sub.2[Ge.sub.0.95Mn.sup.4+.sub.0.05F.sub.6] had
peaks at the positions in diffraction angle 20 that were
approximately the same as the X-ray diffraction pattern of the
crystal structure model of K.sub.2MnF.sub.6 according to ICDD Card
No. 01-077-2133, from which it was confirmed that the fluoride
fluorescent material of Example 1 had the crystal structure that
was changed from the K.sub.2GeF.sub.6 crystal structure to the
crystal structure similar to the K.sub.2MnF.sub.6 crystal
structure.
[0103] As shown in FIG. 6, the fluoride fluorescent material of
Reference Example 1 having a composition represented by
K.sub.2SiF.sub.6:Mn.sup.4+ had no light emission peak in a range of
615 nm or more and less than 625 nm, or had only a small peak
therein that could not be recognized as a peak. As shown in FIG. 7,
the fluoride fluorescent material of Reference Example 2, which was
obtained by bringing the fluoride fluorescent material of Reference
Example 1 into contact with the fluorine-containing substance and
subjecting to the heat treatment in an inert gas atmosphere at
400.degree. C., also had no light emission peak in a range of 615
nm or more and less than 625 nm, or had only a small peak therein
that could not be recognized as a peak.
[0104] As shown in FIG. 8, the X-ray diffraction pattern of the
fluoride fluorescent material of Comparative Example 1 having a
composition represented by K.sub.2SiF.sub.6:Mn.sup.4+ and the X-ray
diffraction pattern of the fluoride fluorescent material of
Comparative Example 2 obtained by subjecting the fluoride
fluorescent material of Comparative Example 1 to the heat treatment
had peaks at the positions in diffraction angle 20 that were
approximately the same as each other, from which no change in
crystal structure by the heat treatment was confirmed.
[0105] The fluoride fluorescent material of the present disclosure
can be favorably applied particularly to light sources using a
light emitting diode as an excitation light source, such as light
sources for illumination, light sources for an image display
device, e.g., an LED display and a backlight for a liquid crystal
display, traffic signals, illuminated switches, various sensors,
various indicators, small-sized strobe lights.
* * * * *